It is well known that an alkylaryl carbonate undergoes disproportionation to give a diaryl carbonate and a dialkyl carbonate as shown by reaction formula (I): ##STR1## wherein R represents an alkyl group; and Ar represents an aryl group (hereinafter the same).
It is also well known that an interesterification reaction between an alkylaryl carbonate and an aromatic hydroxy compound yields a diaryl carbonate as shown by reaction formula (II): ##STR2##
Accordingly, an alkylaryl carbonate is indispensable for production of a diaryl carbonate.
An alkylaryl carbonate can be obtained by reacting a dialkyl carbonate and an aromatic hydroxy compound in the presence of a catalyst as depicted by reaction formula (III): ##STR3##
The reactions represented by formulae (I) to (III) are equilibriumreactions with the equilibriumbeing shifted to the original system. Conventional studies on these reactions have been directed chiefly to development of catalysts (see JP-A-51-75044 (which corresponds to U.S. Pat. No. 4,045,464) (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-51-105032 (which corresponds to U.S. Pat. No. 4,182,726), JP-A-54-48733, JP-A-60-169444, JP-A-60-169445 (which corresponds to U.S. Pat. No. 4,552,704), JP-A-56-25138, JP-A-57-176932, JP-A-57-183745, JP-A-60-173016 (which corresponds to U.S. Pat. No. 4,609,501), JP-A-1-93560, JP-A-1-265064, and JP-A-1-265064).
Further, in order to help the reaction proceed, it has been proposed to install a distillation tower on the reactor to drive a by-produced alcohol or a carbonate out of the reaction system while conducting the reaction in a batch system (see JP-B-61-25696 (the term "JP-B" as used herein means an "examined published Japanese patent application"), JP-A-60-173016, JP-A-60-169445, JP-A-60-169444, JP-A-56-123948 (which corresponds to U.S. Pat. No. 4,182,726), JP-A-56-25138, JP-A-54-48733, JP-A-54-48732, JP-A-51-105032, and JP-A-51-75044).
It has also been proposed to produce an alkylaryl carbonate and/or a diaryl carbonate by feeding a dialkyl carbonate, an aromatic hydroxy compound, and a catalyst to a multi-plate distillation tower being continuously operated as described in JP-A-3-291257 (which corresponds to U.S. Pat. No. 5,210,268).
However, since the above process attains only a low conversion, large quantities of unreacted dialkyl carbonate and aromatic hydroxy compound separated from the produced aromatic carbonates should be returned to the reaction system. That is, the process requires not only large-sized equipment but increased cost for separation of unreacted materials from the produced aromatic carbonates and is therefore unsuited to industrial production of aromatic carbonates.
It is also well known that an alkylaryl carbonate easily undergoes decarboxylation to produce an alkylaryl ether as is mentioned in JP-A-51-75044. Therefore, heating for a long time causes an untoward side reaction, resulting in a reduction in yield of a diaryl carbonate.
In order to overcome this problem, it has been suggested to carry out the disproportionation reaction of an alkylaryl carbonate (formula (I)) by feeding an alkylaryl carbonate and a catalyst to a multi-plate distillation tower being continuously operated as described in JP-A-4-9358 (which corresponds to U.S. Pat. No. 5,210,268).
However, where a mixture of a dialkyl carbonate, an aromatic hydroxy compound and a catalyst or a mixture of an alkylaryl carbonate and a catalyst is fed to a multi-plate distillation tower in continuous operation as described above, the catalyst precipitates to clog the distillation tower during long-term operation. If a distillation tower in continuous operation is clogged, the tower must be dismantled and cleaned. Dismantling and cleaning of a distillation tower are economically disadvantageous as involving much time and labor. Besides, periodical shut-down of the production line for dismantling and cleaning of a distillation tower involves non-routine work such as resumption and shut-down of equipment, which is unfavorable from the safety consideration.